The terrible events of today - five deaths and 40 injured - remind me of the days when I worked in London. Then the threat was the bombs of the IRA, and you can still see the transparent plastic rubbish bins that replaced the metal ones to make it harder to plant a bomb. And we occasionally heard a bomb going off.
But today there's a silver lining. The murderer (I don't actually know just yet whether he was a terrorist or just a nutcase) didn't use a bomb; probably had no notion of how to make one. All he could use was a car and a knife. Because anyone can get a car and a knife.
In America, pretty much anyone can buy a semi-automatic rifle, which can fire as quickly as you press the trigger. And, of course, any amount of ammunition that you like. If the murderer had had access to explosives and guns, the butcher's bill would have been much higher.
In America, some folks argue that you're killed just as dead with a knife as with a gun. They're missing the point. Access to guns increases the casualty count.